In 1967 he delivered his habilitation thesis „Materials for the Analysis of Social Change“ („Materialien zur Analyse des sozialen Wandels“), which was distributed as a hectograph.
During the early 1970s in co-operation with economists from the Goethe University Frankfurt he organized the SPES project (Sozialpolitisches Entscheidungs- und Indikatorensystem, Sociopolitical Decision Making and Indicator System).
This project in 1979 was continued by the Special Research Group 3 Microanalytic Foundations of Societal Policies, Frankfurt/Mannheim (Sonderforschungsbereichs 3 „Mikroanalytische Grundlagen der Gesellschaftspolitik“).
In September 1987 Zapf was appointed scientific manager (president) of the Wissenschaftszentrums Berlin für Sozialforschung (WZB); he held this office until 31 August 1994.
From 1976 to 1985 he was a member of the Senate Commission for Empirical Social Research (Senatskommission für Empirische Sozialforschung der DFG).
From 1987 to 1909 Zapf was co-editor of the „Zeitschrift für Soziologie“, was an advisory member of Social Indicators Research and grant evaluator of the Alexander von Humboldt Foundation.
New lands within sociology with respect to analysis of large data sets were beaten by Zapf‘s assistants Johann Handl, Karl Ulrich Mayer and Walter Müller in the SPES-project to exploit the supplementary survey to the microcensus 1971 which resulted in the publication „Class Positions and Social Structure“ („Klassenlagen und Sozialstruktur“),[5] being the first class analysis for Germany with micro data.
The central publication – based on exploitations of this survey – was „Quality of Life in the Federal Republic of Germany: Objective Living Conditions and Subjective Well-being“ („Lebensqualität in der Bundesrepublik: Objektive Lebensbedingungen und subjektives Wohlbefinden“) (1984).
Zapfs movement to the WZB Berlin in 1987 and the collapse of the German Democratic Republic (GDR) opened new research fields.
The collapse of the Socialist economic system offered possibilities to him to expand his theoretical notions, e.g. by the concept of „modernization made good“ („nachgeholte Modernisierung“).
[7] This new interpretation of modernization theory is less ethnocentric and path dependent, and is also sensitive towards failures and shydy sides (e.g. environmental hazard, competition in armaments, external economic effects of Western industrialized countries).
If we want to admit Rucht to speak,[8] then societal modernization „is a variant-rich and in no way a linear evolution, characterized by uncoincident processes, step backs and contradicting changes in parts of the social system“.
Zapf was successful in promoting and placing young sociologists: thus, among his former students and research assistants are Karl Ulrich Mayer, Walter Müller, Peter Flora, Johann Handl, Jens Alber, Wolfgang Glatzer, Heinz-Herbert Noll, Jürgen Kohl, Roland Habich, Franz Rothenbacher and many others.